Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:
3GPPthird generation partnership projectACKacknowledgeBPSKbinary phase shift keyingCPcyclic prefixCSIcyclic shift indexDLdownlinkDM RSdemodulation reference symbolseNBE-UTRAN Node B (evolved Node B)HARQhybrid automatic repeat requestLTElong term evolution (also known as E-UTRAN or 3.9G)MACmedium access controlMU-MIMO multi-user multiple input/multiple outputNACKnot acknowledge or negative acknowledgementNode Bbase stationOFDMAorthogonal frequency division multiple accessPDCPpacket data convergence protocolPHICH physical hybrid ARQ indicator channelPHYphysicalPRBphysical resource blockQPSKquadrature phase shift keyingRFrepetition factorRLCradio link controlRRCradio resource controlSC-FDMAsingle carrier, frequency division multiple accessSFspreading factorUEuser equipmentULuplinkUTRANuniversal terrestrial radio access network
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. The current working assumption is that the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
One specification of interest to these and other issues related to the invention is 3GPP TS 36.300, V8.3.0 (2007-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8).
FIG. 1 reproduces FIG. 4 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC (Evolved Packet Core), more specifically to a MME (Mobility Management Entity) by means of a S1-MME interface and to a Serving Gateway (S-GW or access gateway) by means of a S1-U interface. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNBs.
The eNB is of interest to certain exemplary embodiments of this invention, and hosts the following functions:                functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);        IP header compression and encryption of user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        measurement and measurement reporting configuration for mobility and scheduling.        
Other documents of interest herein include 3GPP TSG RAN1 #51, R1-074588, Jeju, Korea, Nov. 5-9, 2007, Source: Motorola, Title: PHICH Assignment in E-UTRA (referred to hereafter as R1-074588), and 3GPP TSG RAN WG1 Meeting #51 bis, R1-080301, Sevilla, Spain, Jan. 14-18, 2008, Source: Nokia, Nokia Siemens Networks, Title: PHICH and mapping to PHICH groups (referred to hereafter as R1-080301).
In a wireless system such as LTE, and in the case of UL transmission with HARQ, the eNB will transmit an ACK/NACK in response to receiving an UL transmission from the UE. In accordance with recent decisions within 3GPP (January 2008 meeting in Seville) for LTE no option will be provided for not transmitting the PHICH. This implies that the PHICH resources need to be defined and used for all eNB and UE configurations. The eNB may in some circumstances need to simultaneously transmit ACK/NACKs corresponding to two or more UL transmissions. As a result, a given UE needs to determine which ACK/NACK transmitted in a certain PHICH channel corresponds to the UL transmission made by that UE.
There are several possible uses cases that need to be considered. These include UEs which are dynamically scheduled (with a scheduling grant), UEs that are persistently scheduled or that are using non-adaptive HARQ (no scheduling grant), and MU-MIMO UEs (overlapping PRB allocations).
In R1-080301 it was proposed to tie/link the PHICH channel/resources to the actual physical resources used for the UL transmissions.
Another approach is described in R1-074588, where for dynamic scheduling (transmission assigned with a scheduling grant) UEs are divided to one or more groups and for each UE group a PHICH group is assigned.
Note in this regard that a PHICH group corresponds to physical resources that can, at most, carry eight ACK/NACKs when a short CP is used, and fewer ACK/NACKs when a longer CP is used. It may be assumed that the UE knows the ACK/NACK resources within the PHICH group from the CSI of the DM RS, which is signaled to the UE in an UL grant for the corresponding UL transmission.
The PHICH group containing a maximum of eight PHICH is formed using spreading and repetition. For example, in the case of a normal CP the SF is 4 (for 4 sub-carriers) and the RF is 3, thus this particular PHICH group occupies 12 sub-carriers.
It has been agreed in 3GPP that the PHICH group will have eight BPSK modulated symbols which can be independently modulated on inphase (I) and quadrature (Q) branches. The BPSK modulated symbols will carry the information from eight PHICH channels. The eight PHICH symbols in a PHICH group will be distributed in frequency for diversity purposes, and may also be distributed in time for power balancing purposes (depending on the system configuration).
At least one problem exists in that at present there is no technique available for mapping from the physical resources (potentially including a PHICH index modifier) to the actual PHICH resources.